Synthetic gypsum fertilizer product and method of making

ABSTRACT

Embodiments of the invention are directed to pelletized synthetic gypsum and methods and systems for producing pelletized synthetic gypsum. Synthetic gypsum is combined with a binder composition and pelletized to a desired size. The binder composition may include lignosulfonate. Additives may be included in the pellets such as various plant nutrients and micro-nutrients. An additive may include elemental sulfur. The resulting pellets may have a mean pellet size guide number (SGN) from approximately 150 to approximately 300 and a crush strength from approximately 2 lbf to approximately 12 lbf

BACKGROUND

Industrial process plants for chemical manufacturing and power plantsoften produce a calcium sulfate by-product or co-product referred toherein as synthetic gypsum. Synthetic gypsum, produced by power plants,sometimes referred to as flue-gas desulfurization (“FGD”) gypsum, is aby-product recovered from flue gas streams resulting from the burning ofenergy sources containing concentrations of sulfur (e.g., coal).Synthetic gypsum is normally produced from scrubbing the flue gas streamwith a limestone slurry that will capture the sulfur released from thefuel burned in the boiler. The limestone slurry and captured sulfur canbe dewatered to separate the liquids and solids to create a calciumsulfate product that is referred to as “synthetic gypsum”.

In contrast to synthetic gypsum, “natural gypsum” is mined fromnaturally occurring deposits in various regions of the world. In mostcases, natural gypsum is formed as sea water evaporates. Capillaryaction brings saline water to the surface where the salts areprecipitated. As such, natural gypsum is generally found in layersformed under salt water. In addition to the wallboard industry andcement manufacturing, natural gypsum is also utilized in agriculture ascalcium and sulfur are two key nutrient components needed by plants.More specifically, natural gypsum and can contain calcium sulfate atvarying concentrations, usually at less moisture content and lowercalcium sulfate purity as compared to synthetic gypsum. Natural gypsum,because of its lower moisture content and free flowing granular form,can be easier to spread with conventional farm equipment. Becausenatural gypsum has insoluable mineral components and also solubilizesrather slowly, natural gypsum can provide a slow continual release oflow level sulfur to the soil for more than just the year it is applied.However, this slow release of sulfur can reduce the availability of thesulfur from natural gypsum when it is needed to promote plant growth,which can be a disadvantage since the sulfur is not readily availableand, thus, leaches through the soil without adding nutrients to theplant at the time period when needed.

Synthetic gypsum is unique in that the industrial process from which itis derived causes the calcium sulfate to have a very fine particle sizetypically in the range of 5 to 150 micron and, therefore, it has greatersurface area and retains moisture from the dewatering process.Disadvantageously, fine particle minerals are known to have difficultphysical handling properties when they contain moisture causing thematerials to stick to material handling equipment and spreading devices.The finer particle size causes the moisture to be difficult to separatefrom the solid particles. Although FGD systems can generate largequantities of synthetic gypsum products, because of the difficultphysical handling properties, only a portion of the synthetic gypsumproduced can be beneficially recycled for use in the wallboard industry.Lesser quantities of synthetic gypsum are processed and utilized in thecement manufacturing industry. The remaining synthetic gypsum must beplaced in landfills or deposited in surface impoundments. Since theproduction of synthetic gypsum is rapidly increasing as new scrubbersare added to new or existing power plants in order to comply withfederal, state or local air pollution control regulations, a need existsto increase the beneficial uses of synthetic gypsum.

BRIEF SUMMARY

Embodiments of the invention are directed to processing and forming,which can include pelletizing, granulating, or extruding, syntheticgypsum and methods and systems for producing pelletized syntheticgypsum. In a first aspect of the invention, a method of producing afertilizer is provided. The method includes processing the syntheticgypsum and then discharging the processed synthetic gypsum onto aforming device, which may comprise a pelletizer, granulator, orextruder. The method further includes feeding a binder composition tothe processing equipment and/or forming device. Additionally, the methodincludes pelletizing the material fed to the pelletizer to a mean pelletsize guide number (“SGN”) from approximately 150 to approximately 300.In some embodiments, the mean pellet SGN is from approximately 250 toapproximately 280. The resulting pelletized synthetic gypsum has a crushstrength from approximately 2 pound-force (“lbf”) to approximately 12lbf. In another embodiment, the resulting pelletized synthetic gypsumhas a crush strength from approximately 3 lbf to approximately 8 lbf. Inanother embodiment, the resulting pelletized synthetic gypsum has acrush strength from approximately 4 lbf to approximately 6 lbf.

In some embodiments of the method, the synthetic gypsum fed to theforming device has a mean particle size of less than 100 microns.

In some embodiments of the method, the binder composition includes awater soluble binder. In some embodiments, the binder compositionincludes a water soluble binder that comprises, or is one or more of thegroup consisting of, brewers condensed solubles, lignosulfonate, sodiumcarbonate lignin, cane molasses, beet syrup, beet molasses, desugaredbeet molasses, whey, starch, starch derivatives, soy solubles with canemolasses, hydrolyzed collagen, amino acid solutions, cellulosederivatives, or cellulose based polymer binders. The lignosulfonate maybe a calcium lignosulfonate.

In some embodiments, the method further includes feeding an additive tothe mixer or to the forming device. The additive can include at leastone of finely ground calcium carbonate, calcium bentonite, kaolin clays,manganese, zinc, boron, calcium, copper, and elemental sulfur. Inparticular embodiments, the additive includes elemental sulfur.

In another aspect of the invention, a fertilizer is provided. Thefertilizer includes pellets. The pellets include synthetic gypsum and abinder composition. The pellets have a mean pellet SGN fromapproximately 150 to approximately 300. In some embodiments the mean SGNis from approximately 250 to approximately 280. The resulting pelletizedsynthetic gypsum has a crush strength from approximately 2 lbf toapproximately 12 lbf. In another embodiment, the resulting pelletizedsynthetic gypsum has a crush strength from approximately 4 lbf toapproximately 8 lbf. In another embodiment, the resulting pelletizedsynthetic gypsum has a crush strength from approximately 4 lbf toapproximately 6 lbf.

In some embodiments of the fertilizer, the binder composition includes awater soluble binder. In some embodiments, the binder compositionincludes a water soluble binder that comprises, or is one or more of thegroup consisting of, brewers condensed solubles, lignosulfonate, sodiumcarbonate lignin, cane molasses, beet syrup, beet molasses, desugaredbeet molasses, whey, starch, starch derivatives, soy solubles with canemolasses, hydrolyzed collagen, amino acid solutions, cellulosederivatives, or cellulose based polymer binders. The lignosulfonate maybe a calcium lignosulfonate.

In some embodiments of the fertilizer, the pellets further include anadditive. The additive can include at least one of finely ground calciumcarbonate, calcium bentonite, kaolin clays, manganese, zinc, boron,calcium, copper, and elemental sulfur. In particular embodiments, theadditive includes elemental sulfur. In particular embodiments, theadditive includes elemental sulfur.

In another aspect of the invention, a process for producing a fertilizeris provided. The process includes feeding synthetic gypsum to a dryer,feeding dried synthetic gypsum and a binder composition to a mixer,mixing the material fed to the mixer, feeding the mixed material to aforming device, pelletizing the material fed to the forming device,feeding the pelletized material to a dryer, drying the pelletizedmaterial, feeding the dried pelletized material to a screener, andscreening the dried pelletized material fed to the screener to a meanpellet SGN from approximately 150 to approximately 300. In someembodiments, the mean SGN is from approximately 250 to approximately280. The process further includes recycling unders and overs removedduring screening to the mixer. The resulting pelletized synthetic gypsumhas a crush strength from approximately 2 lbf to approximately 12 lbf.In another embodiment, the resulting pelletized synthetic gypsum has acrush strength from approximately 3 lbf to approximately 8 lbf. Inanother embodiment, the resulting pelletized synthetic gypsum has acrush strength from approximately 4 lbf to approximately 6 lbf.

In some embodiments of the process, the synthetic gypsum fed to themixer has a mean particle size of less than 100 microns.

In some embodiments of the process, the binder composition includes awater soluble binder. In some embodiments, the binder compositionincludes a water soluble binder that comprises, or is one or more of thegroup consisting of, brewers condensed solubles, lignosulfonate, sodiumcarbonate lignin, cane molasses, beet syrup, beet molasses, desugaredbeet molasses, whey, starch, starch derivatives, soy solubles with canemolasses, hydrolyzed collagen, amino acid solutions, cellulosederivatives, or cellulose based polymer binders. The lignosulfonate maybe a calcium lignosulfonate.

In some embodiments, the process further includes feeding an additive tothe mixer. The additive can include at least one of finely groundcalcium carbonate, calcium bentonite, kaolin clays, manganese, zinc,boron, calcium, copper, and elemental sulfur. In particular embodiments,the additive includes elemental sulfur.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described embodiments of the invention in general terms,reference will now be made to the accompanying drawings, where:

FIG. 1A is a 100 times magnification illustration of natural gypsum, inaccordance with embodiments of the present invention;

FIG. 1B is a 100 times magnification illustration of synthetic gypsum,in accordance with embodiments of the present invention; and

FIG. 2 illustrates a process for pelletizing synthetic gypsum, inaccordance with embodiments of the present invention.

FIG. 3 illustrates two (2) processes for drying synthetic gypsum, inaccordance with embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Embodiments of the present invention now may be described more fullyhereinafter with reference to the accompanying drawings, in which some,but not all, embodiments of the invention are shown. Indeed, theinvention may be embodied in many different forms and should not beconstrued as limited to the embodiments set forth herein; rather, theseembodiments are provided so that this disclosure may satisfy applicablelegal requirements. Like numbers refer to like elements throughout.

Synthetic gypsum is generally produced in limestone-forced oxidationscrubbers that remove sulfur dioxide from the flue gas stream after coalcombustion. In general, a wet scrubbing process first exposes the fluegases to a slurry of hydrated lime. The lime slurry is formed bygrinding limestone to a small particle size and combining the powderedlimestone with water to make a mixture that can be pumped at regulatedflow rates to the scrubber equipment. Capture of sulfur by the limeslurry occurs in an absorber vessel and initially forms calcium sulfite(CaSO₃.5H₂O). The scrubber slurry is then transferred to a storage tankwhere the aeration occurs. Forcing additional air into the systemoxidizes the calcium sulfite and converts it into gypsum, i.e.,CaSO₄.2H₂O that results in solids concentration. The higher solidsgypsum is pumped to a dewatering system. At the dewatering portion ofthe gypsum handling process the gypsum is dewatered and washed to removewater-soluble salts and elements such as sodium chlorides, potassiumchlorides and boron (B). Dewatering can also take place during theoxidation process. Generally, the final step of the gypsum productionprocess involves partial removal of water by a combination ofcentrifugation and vacuum filtration so that the synthetic gypsum as amoisture content of approximately 6% to approximately 16%. The syntheticgypsum that is recovered is high quality and suitable for variousindustrial (e.g., wallboard) uses. As noted above, the supply ofsynthetic gypsum is increasing due to more stringent environmentalregulations coupled with the addition of new equipment at coal-firedpower plants.

While synthetic gypsum and natural gypsum generally have similarchemical properties (i.e., calcium and sulfur percentage compositions),synthetic gypsum cannot be effectively utilized in the agricultureindustry due to its difficult material handling properties. Syntheticgypsum and natural gypsum have other material differences. Syntheticgypsum typically has a higher purity of CaSO4 in comparison to naturalgypsum. Synthetic gypsum production also yields much smaller particlesizes than the natural gypsum that is mined. Most synthetic gypsum has aparticle size less than 250 microns and often includes particle sizesless than 200 microns, less than 150 microns, less than 100 microns, andeven less than 50 microns. Indeed, most synthetic gypsum has particlesizes in the range of approximately 5-150 microns. FIG. 1A illustrates a100× magnification of typical natural mined gypsum. By comparison, FIG.1B illustrates a 100× magnification of typical synthetic gypsum. Asillustrated, synthetic gypsum obtained is generally multiple orders ofmagnitude smaller than natural mined gypsum. As an example, an analysisof synthetic gypsum from a power plant in Ohio (which is typical ofsynthetic gypsum) in comparison with natural gypsum mined in Ohioproduced the following results:

TABLE 1 Comparison of Synthetic Gypsum and Natural Gypsum Particle SizeParticle Size Synthetic Gypsum (%) Natural Gypsum (%)   >250 microns0.14 100 150-250 microns 3.2 0 105-150 microns 33 0  74-105 microns 33 0   <74 microns 31 0

Due to the small particle sizes of synthetic gypsum, its moistureretention and resultant difficulty in material handling, agriculturalapplicability is minimal due to difficulties of feeding synthetic gypsumthrough spreading equipment onto or into the soil. Within theagriculture industry typical spreading equipment are designed to handlegranular materials and are not capable of spreading such small particlesthat stick together. Synthetic gypsum, if it could be effectively spreadas an agricultural product, is a soluble source of the essential plantnutrients, calcium and sulfur, that would improve overall plant growthand also would improve the physical properties of some soils (especiallyheavy clay soils). Advantageously, the present invention provides apelletized, granulated, or extruded synthetic gypsum that will promotesoil aggregation and, thus, will (1) help prevent dispersion of soilparticles, (2) reduce surface crust formation, (3) promote seedlingemergence, and (4) increase water infiltration rates and movementthrough the soil profile. The pelletized, granulated, or extrudedsynthetic gypsum of the present invention also reduces erosion losses ofsoils and nutrients and reduce concentrations of soluble phosphorus insurface water runoff. Chemical properties improved by application of thepelletized, granulated, or extruded synthetic gypsum of the presentinvention include the mitigation of subsoil acidity and aluminumtoxicity. This enhances deep rooting and the ability of plants to takeup adequate supplies of water and nutrients during drought periods. Thepelletized, granulated, or extruded synthetic gypsum of the presentinvention can also be used for sodic soil reclamation and can also beincluded as a component in synthetic soils for nursery, greenhouse, andlandscape use.

Embodiments of the present invention are directed to reducing themoisture content and increasing the particle size of synthetic gypsumand improving its ease of spreading while maintaining the beneficialproperties. Significant properties of pelletized synthetic gypsum foruse as fertilizer include particle size and crush strength. Desirableparticle sizes in some embodiments have a mean pellet SGN ofapproximately 100 to approximately 500, in some embodiments fromapproximately 100 to approximately 300, in some embodiments fromapproximately 150 to approximately 300, in some embodiments fromapproximately 200 to approximately 300, in some embodiments fromapproximately 250 to approximately 350, and in some embodiments fromapproximately 250 to approximately 280. SGN is utilized generally in thefertilizer industry and is simply the diameter of the median granulesize and is expressed in millimeters multiplied by 100. For example, ameasurement of an SGN of 250 would correspond to a median granule sizeof 2.50 millimeters. Desirable crush strengths in some embodiments arefrom approximately 1 lbf to approximately 12 lbf, in some embodimentsfrom approximately 2 lbf to approximately 10 lbf, in some embodimentsfrom approximately 2 lbf to approximately 8 lbf, in some embodimentsfrom approximately 3 lbf to approximately 8 lbf, in some embodimentsgreater than 2 lbf, in some embodiments greater than 3 lbf, and in someembodiments greater than 5 lbf. Another desirable measure of crushstrength is the ability of the synthetic gypsum pellets of the presentinvention to substantially maintain integrity when being spread using anapproximately 700 rotation per minute (“rpm”) impeller up to anapproximately 800 rpm impeller. Advantageously, such the syntheticgypsum pellets of the present invention are capable of being spread fromapproximately 60 feet to 100 feet, or in other embodiments, 70 feet to90 feet or in still other embodiments 80 feet to 100 feet.

In order to achieve desired physical properties of the pellet, one ormore binder additives may be utilized. In one embodiment, the bindercomposition includes a water soluble binder. In some embodiments, thebinder composition includes a water soluble binder that comprises, or isone or more of the group consisting of, brewers condensed solubles,lignosulfonate, sodium carbonate lignin, cane molasses, beet syrup, beetmolasses, desugared beet molasses, whey, starch, starch derivatives, soysolubles with cane molasses, hydrolyzed collagen, amino acid solutions,cellulose derivatives, or cellulose based polymer binders. Thelignosulfonate may be a calcium lignosulfonate.

Lignosulfonates, which are water-soluble anionic polyelectrolytepolymers. Lignosulfonates may vary in molecular mass from about 1,000 toabout 140,000. An exemplary lignosulfonate is Norlig A™ calciumlignosulfonate solution supplied by LignoTech USA, Houston, Tex. In someembodiments, it is desirable for the amount (wt. %) of lignosulfonate inthe final pellet to be at least approximately 1%, in some embodimentsfrom approximately 1% to approximately 5%, and in some embodimentsapproximately 2%.

FIG. 2 illustrates one embodiment of a process for forming syntheticgypsum pellets. Synthetic gypsum is inputted into a dryer 10, throughfeed line 1, to reduce the moisture content and then introduced into amixer 20, such as a paddle/pin via feed line 4. A binder is introducedto the mixer 20 via feed line 2. Additional additives (if desired) maybe introduced via feed line 3. A recycle line 10 may also input materialinto the mixer 20. While FIG. 2 illustrates separate feed lines, it willbe appreciated that the components may be input separately through thesame feed line(s) or at the same time through the same feed line(s).While a paddle/pin mixer 20 is described, it will be appreciated thatany suitable mixer type may be utilized to mix the synthetic gypsum,binder, and optional additional additives.

In one embodiment, a pin mixer is used in which dried synthetic gypsumhaving a density of 50 lbs/ft³ to 65 lbs/ft³ is fed at a rate ofapproximately 10 tons per hour (“tph”) to approximately 18 tph. A binderof lignosulfonate having 18% to 48% solids is fed into the pin mixer ata rate of approximately 1 gallon per minute (“gpm”) to approximately 8gpm at a pressure of 35 psi to 55 psi. The spray location in oneembodiment is +2, −6. The pin mixer mixes the contents at a speed of 250rpm to 480 rpm and, in one embodiment, at 278 rpm. The synthetic gypsummixture exits the pin mixture with a moisture content of 4% to 8%.

Regarding the drying step, synthetic gypsum may be converted into one oftwo hemihydrate forms of calcium sulfate (CaSO4.½H2O) through a seriesof one or more drying processes. FIG. 4 illustrates a general processflow for executing the conversion of synthetic gypsum into hemihydrate.First, the synthetic gypsum may be dried. The purpose of drying thesynthetic gypsum may be to remove free moisture from the raw material.Drying the synthetic gypsum may reduce its weighted moisture contentfrom a typical range of approximately 6% to approximately 16% to lessthan approximately 1%. In some embodiments, a direct gas fired dryer ora rotary dryer may be utilized to dry the synthetic gypsum. The dryermay be configured to maintain a consistent temperature below the gypsumcalcining temperature, the point at which dissociation of combined waterbegins to take place, of approximately 262° F. In one embodiment, thesynthetic gypsum is dried in a direct gas fired flash dryer atapproximately 100° F. for approximately 2 to 20 seconds and, morepreferably, 2 to 12 seconds.

In one optional embodiment, the dried synthetic gypsum may then becalcinated, a heating process wherein calcium sulfate is converted intohemihydrate through the disassociation of water molecules. Calcinationmay be performed, for example, by flash drying at high temperatures,cooking in large kettles, heating in furnaces or rotary kilns, usingsteam, cooking in aqueous suspensions, or the like. Typically, two typesof hemihydrate can be formed from dried synthetic gypsum, namelyalpha-hemihydrate and beta-hemihydrate.

Alpha-hemihydrate may be obtained by calcinating synthetic gypsum in apressurized environment. Synthetic gypsum may be injected into apressurized reactor configured to maintain a typical pressure range of14.7 psia (1 atmosphere) to 55.3 psia (3.8 atmospheres). A fluid, suchas pressurized air, steam, water, or combustion gases, may be injectedinto the reactor for creating a fluidized bed of gypsum, controllinghumidity in the reactor, and/or for heating purposes. The temperaturewithin the reactor may be monitored or controlled to maintain atemperature range from approximately 250° F. to 350° F. with a preferredtemperature for inducing the disassociation of water molecules beingbetween 280° F. and 300° F. Typically, the temperature is raised above262° F., but kept below 325° F., to ensure that no other types ofcalcium sulfates are formed.

Beta-hemihydrates may be obtained by calcinating synthetic gypsum in asimilar process as described above. However, to obtainbeta-hemihydrates, the calcination process may occur in a vacuumenvironment, or at atmospheric pressure (e.g., 1 atmosphere). Typically,the temperature is maintained at or near 200° F. to induce thedisassociation of water molecules.

Upon the disassociation of water molecules, the calcinated syntheticgypsum may be converted into alpha- or beta-hemihydrate forms of calciumsulfate. In some embodiments, the calcination process may includemultiple calcinations. Multiple calcinations may strengthen thehemi-hydrate product. In other embodiments, other temperature and/orpressure ranges may be used to convert the synthetic gypsum intohemihydrate, and the calcination process may be conducted over apredetermined period of time or on a time schedule.

FIG. 3 illustrates a general process flow for the conversion ofsynthetic gypsum into hemihydrate. At block 302, the process includesreceiving synthetic gypsum. At block 304, the process includes dryingthe synthetic gypsum via a dryer, wherein the dryer is a direct gasfired dryer or a rotary dryer configured to maintain a consistenttemperature below 262° F. At block 306 the process includes calcinatingthe dried synthetic gypsum, wherein calcinating the dried syntheticgypsum includes one of two processes.

To generate alpha-hemihydrate, at block 308, the process includesinjecting the dried synthetic gypsum into a pressurized reactorconfigured to maintain a consistent pressure between 14.7 and 55.3 psia(between 1 and 3.8 atmospheres). At block 310, the process includesmaintaining a consistent temperature between 250° F. and 350° F. Atblock 312, the process includes inducing the disassociation of watermolecules in the synthetic gypsum. At block 314, the process includesconverting the synthetic gypsum into alpha-hemihydrate.

To generate beta-hemihydrate, at block 316 the process includesinjecting the dried synthetic gypsum into a vacuum or non-pressurizedreactor configured to maintain consistent atmospheric pressure. At block318, the process includes maintaining a consistent temperature atapproximately 200° F. At block 320, the process includes inducing thedisassociation of water molecules in the synthetic gypsum. At block 322,the process includes converting the synthetic gypsum intobeta-hemihydrate.

While not illustrated in FIG. 2, it may be desirable to exclude a dryingstep for the synthetic gypsum prior to input into the mixer 20.Typically, synthetic gypsum produced has a moisture content of greaterthan about 6%, and in some embodiments from approximately 8% toapproximately 16%. In some embodiments, it is desirable to dry thesynthetic gypsum to a moisture content of less than about 10%, in someembodiments less than about 7%, in some embodiments, less than about 5%,in some embodiments less than about 3%, and in some embodiments lessthan about 1%. In some embodiments, the synthetic gypsum is dried toapproximately 1% moisture content prior to mixing/pelletizing.

Once mixed, the material exits the mixer 20 via line 5 and enters theforming device 30. The forming device 30 may comprise a pelletizer, agranulator or an extruder. As used herein, a “pellet” means a fertilizerproduct made by a pelletizer, granulator, or extruder. The pelletizermay be any type of pelletizer such as disc/pan pelletizer, flat diepelletizer, ring die pelletizer, screw press pelletizer, hydraulicpelletizer, or the like. In other embodiments a granulator or extrudermay be used instead of a pelletizer. Additional binder may be introducedto the forming device 30 via line 2 if necessary. Typically, the binderis introduced into the forming device 30 via a spray system so as toconduct the addition of the binder in as uniform manner as possible.

In one embodiment, a pelletizer is used in which mixed synthetic gypsumis fed at a rate of approximately 10 tph to approximately 18 tph. Thefeed location in one embodiment is +2, −3. A binder of lignosulfonatehaving 18% to 48% solids is fed into the pelletizer at a rate ofapproximately 1 gallon per minute (“gpm”) to approximately 8 gpm at apressure of 35 psi to 55 psi. The spray location in one embodiment is+2, −6, −3, −10, −2, −8. The pelletizer pelletizes the mixed syntheticgypsum and binder using a pan rate of 5 rpm to 12 rpm at an angle of 50degrees to 68 degrees. The synthetic gypsum pellets exit with a moisturecontent of 4% to 12%.

After pellet formation, the pellets exit the forming device 30 via line6 and enter dryer 40 to remove excess moisture. The dryer 40 may be anytype of dryer such as a rotary dryer, fluid bed dryer, drum dryer, orthe like. Once the pellets have been dried, they exit the dryer 40 vialine 7 and enter a screener 50. The screener acts to screen out pelletsthat are too large or too small as desired. Typical screeners includevibrating screeners, rotary screeners, and the like. The final productexits the screener via line 8 to storage container 60. Overs (i.e.,pellets larger than specification) and unders (i.e., pellets smallerthan specification) exit the screener and may be recycled to the mixer20 via line 10. Typically, the overs and unders are first introduced toa crusher, such as a hammermill, 70 via line 9 prior to recycling backto the mixer 20.

In some embodiments, it may be desirable to add a micronutrient mix tothe synthetic gypsum for an improved fertilizer product. It iscontemplated that any material may be added to the synthetic gypsumprior to forming depending upon the desired final product. Non-limitingexample additives include calcium carbonate, kaolin clays, zinc,manganese, iron, copper, boron, carbon, chromium, lime, and humic acid.One exemplary additive is Wolf Trax Cropmix DDP available from Wolf TraxInc., Winnipeg, Manitoba, Canada. Cropmix DDP contains 2% boron, 1%copper, 1% iron, 18% manganese, and 17% zinc.

In some exemplary embodiments, elemental sulfur is utilized as anadditive. The use of elemental sulfur provides unique benefits to thefertilizer product. As noted above, sulfur is an important nutrientneeded by plants. However, sulfur is only absorbed by plant-life insulfate (SO₄) form. Elemental sulfur, when added to the soil, willslowly oxidize into sulfate form. The rate of oxidation may vary due tonumerous factors such as microbiological population of the soil, thephysical properties of the elemental sulfur source, and environmentalconditions of the soil including temperature, soil moisture andaeration, soil pH, and fertility status of the soil. As elemental sulfurslowly oxidizes, it provides a continuous supply of sulfate to theplants. As such, a fertilizer that includes synthetic gypsum withelemental sulfur as an additive has the beneficial property of a “fastrelease” sulfate in the form of the synthetic gypsum with a continuousslow release of sulfate from the oxidation of elemental sulfur.

In some embodiments, the resulting pellet is particularly soluble inwater. A benefit to the small raw material particle size of syntheticgypsum is the ease of dissolving the pellets into water. As noted above,some agricultural uses include applying synthetic gypsum in aqueoussolution and sprayed to the plants. As such, the pelletized syntheticgypsum has the benefit of spreadability via conventional fertilizerspreaders as well as solubility in order to utilize the synthetic gypsumin solution with water.

EXAMPLES Example 1

Pelletization testing was conducted on synthetic gypsum with anobjective to produce synthetic gypsum pellets demonstratingapproximately 0.1 percent attrition loss and 5.9 pounds averagecompression strength, with an approximate 92 percent minus 4× plus 20mesh fraction and about 85 percent in the minus 6× plus 16 mesh range.Approximately 30 gallons of dried synthetic gypsum was tested. Norlig A™calcium lignosulfonate solution was supplied by LignoTech USA as liquidbinder additive.

The synthetic gypsum was analyzed for moisture content and bulk density(see table 2).

TABLE 2 Processed Material Properties Moisture Density (aerated) Density(compacted) Processed Material Content lbs/ft³ lbs/ft³ synthetic 1.5%51.3 73.2 gypsum

A Mars Mineral 8D32L Pin Mixer was utilized for testing the syntheticgypsum, using 25:75 Norlig A™ calcium lignosulfonate solution to wateras liquid binder (see table 3).

A pin mixer is a high speed, conditioning and micro-pelletizing devicethat converts powders into small agglomerates through the action of ahigh speed rotor shaft and pin assembly and the addition of liquids suchas water, binders, oil or surfactants. The 8D32L Pin Mixer has an 8″diameter by 32″ long mixing chamber, with two available binder nozzleports. Its maximum feed throughput is 10 cubic feet per hour.

For each test run, the first port was used for liquid binder addition.The first two numbers of the nozzle tip size represent the angle of theflat spray. The second two numbers indicate the flow rate. The 4001nozzle tip has the capability of applying 0.1 gallons of water perminute in a 40 degree spray pattern at 40 psi. Test parameters andconditions for the pin mixer operation are tabulated below (see table3).

TABLE 3 8D32L Pin Mixer Parameters and Conditions Feed 25:75 Norlig A ™to Water Pin Mixer GP Test Rate Nozzle p Rate f I P T MC ABD Run ft³/hrlbs/min tip PSI gal/min lbs/min RPM A % F HP ° F. % lbs/ft³ 1 6.7 5.754001 3 0.03 0.23 1500 31 63% 12 122 5.4 46.3 p = pressure; f =rotational frequency; I = current; % F = per cent full load current; P =power; GP = green pellet; T = temperature; MC = moisture content; ABD =aerated bulk density

A Mars Mineral DP-14 bench scale disc pelletizer was utilized forfurther testing the 8D32L Pin Mixer discharge, also using 25:75 NorligA™ calcium lignosulfonate solution to water as liquid binder (see table3).

A disc pelletizer is an inclined, slowly spinning pan that rollsparticulates into agglomerates. Both angle and speed are adjustable tocontrol movement of the material. The growth of a pellet is similar tothat of a snowball rolling down a hill, gaining size as it goes. Pelletsize is manipulated by binder spray location, material feed location,pan speed and pan angle. Since gravity is the central force involved,disc pelletizers are efficient machines.

The DP-14 Agglo-Miser has a 14″ diameter pan, the depth of which can beadjusted to 3″, 6″ or 9″. Feed material and liquid binder are addedmanually to model automated systems utilized on larger scale discs ordrums. For disc pelletization, the DP-14 pan depth was adjusted to 3″

The DP-14 disc was operated at the parameters indicated below (see table4). Liquid binder was applied to the feed material in the pan by meansof a plastic spray bottle.

TABLE 4 DP-14 Disc Parameters Feed 25:75 NA to W Pan GP Test MC PositionApplication f Tilt MC ABD Run ID % clock clock in. to p RPM ° % lbs/ft³1A Run 1 Discharge 4.0 5 5 5 32 57 9.0 61.7 MC = moisture content; NA =Norlig A ™ calcium lignosulfonate; W = water; in. to p = inches from panperimeter; f = rotational frequency; GP = green pellet; ABD = aeratedbulk density

Representative green pellets from test run 1A were dried in an 80° C.convection oven and analyzed for moisture content, bulk density,attrition loss, compression strength (see table 4), and particle size(see table 5). A Mettler Toledo HR83-P Moisture Analyzer, set at 80° C.,standard (constant temperature) drying program and switch-off criterion5 (i.e., 1 mg per 140 seconds), was utilized. Bulk density analysis wasconducted on the pellets, as discharged. Attrition analysis measuredpercent losses of minus 10× plus 16 mesh pellets after 5 minutes on a 45mesh screen in a Ro-Tap® test sieve shaker. Compression strengthanalysis was conducted on ⅛ inch diameter pellets.

Representative pin mixer discharge from test run 1, as fed to the DP-14disc, was dried in an 80° C. convection oven and analyzed by formoisture content, bulk density (see table 4), and particle size (seetable 6).

TABLE 5 Pellet Properties % NA Bulk Density Compression Test PelletizerSolids AP (aerated) (compacted) % Attrition intact @ Run Model(s) in DPin AP % MC lbs/ft³ lbs/ft³ Loss n lbs 1A 8D32L to DP-14 1.5% 1.5% 0.1%57.0 63.8 0.7% 3.7 1 8D32L 0.6% 0.6% 0.1% 54.4 n/a n/a n/a NA = NorligA ™ calcium lignosulfonate; DP = (theoretically) dry pellets having 0.0%moisture content; AP = actual pellets as analyzed; MC = moisture content

TABLE 6 Pellet Size Run 1A 8D32L to DP-14 1.5% Norlig A Solids 0.1%Moisture Content Sieve Retained Cumulative  4 mesh 0.7% 0.7%  6 mesh0.4% 1.1% 10 mesh 32.5% 33.5% 16 mesh 62.1% 95.6% 20 mesh 2.4% 98.0% 30mesh 0.1% 98.1% Pan 1.9% 100.0% 96.3% −4 X +20 mesh 93.6% −6 X +16 mesh

TABLE 7 DP-14 Disc Feed Particle Size Run 1 Discharge 0.6% Norlig ASolids 0.1% Moisture Content Sieve Retained Cumulative 16 mesh 10.5%10.5% 20 mesh 5.8% 16.3% 45 mesh 14.6% 30.9% 80 mesh 23.9% 54.8% 120mesh  17.0% 71.7% 200 mesh  17.1% 88.8% Pan 11.2% 100.0%

Pellets matching the size requirement and nearly matching the durabilityrequirement were made from the low moisture synthetic gypsum, utilizing25:75 Norlig A™ calcium lignosulfonate solution to water as liquidbinder, with a Mars Mineral DP-14 Disc Pelletizer, fed with dischargefrom a Mars Mineral 8D32L Pin Mixer (see tables 2 and 3). These pelletsexhibited 0.7 percent attrition loss and 3.7 pounds average compressionstrength (see table 4). Ninety six percent of the pellets, as dischargedfrom the disc pelletizer, were in the minus 4× plus 20 mesh fraction,and nearly 94 percent were in the minus 6× plus 16 mesh range (see table5).

Example 2

Synthetic gypsum sludge with 20% moisture was dried to a 1% moisturepowder. Two parts dried gypsum were blended with one part sludge for ahand mix feed material with 7.5% moisture. Two (2) lbs of hand blendedmaterial was fed to a pin mixer with 0.2 lbs. lignosulfonate with 40%solids. The blended material with addition of the lignosulfonate was awet fluff with no agglomerated particles and 8.5% final dischargemoisture.

The blended material was discharged from the pin mixer to a panpelletizer and sprayed with the same solution of 40% solidslignosulfonate as the material rotated around the pan pelletizer.

Small seed pellets formed and grew uniformly across the pan pelletizerto 5-10 mesh in size. Dried crush strength was measured to be 3-3.5 lbs.It is believed that a higher ratio of dried synthetic gypsum to sludgemay increase crush strength by allowing for increased amounts oflignosulfonate in the final dried pellets.

Example 3

12% moisture synthetic gypsum and dried synthetic gypsum (1% moisture)was tested. In a first run a 50/50 mix of dry and wet synthetic gypsumwas sprayed with lignosulfonate with 2% solids. During the addition oflignosulfonate, the mixture turned to a mud-like consistency and failedto granulate.

In a second run, 2500 g of dry gypsum and 2% solids lignosulfonate (94g) mixed with 100 g. of water was tested. The product granulated verywell and the final crush strength of the pellets were between 3 lbf and8 lbf.

In a third run, 12% moisture synthetic gypsum was combined with an equalamount of bentonite clay. With addition of 2% solids lignosulfonate, theproduct granulated very well and pellets with a crush strength of 8 lbfand 18 lbf was obtained.

While the present invention has been described in connection with theexemplary embodiments thereof, it will be understood that anymodification will be apparent to those of ordinary skill in the art andthat this application is intended to cover any adaptations or variationsthereof. Therefore, it is intended that this invention be limited onlyby the claims and equivalents thereof.

Example 4

Full Scale Testing: Synthetic gypsum was dried from 8%, 10% 12% 14% and16% moistures to less than 2% moisture. Dried gypsum was subsequentlycombined with 1% to 5% calcium bentonite in powder form to create apowder mixture that was fed to a mixer where a binder and water wereadded. The addition of binder liquid concentration varied between 25%and 65% binder and 75% and 35% water. At the mixer the addition ofliquid varied between 1% and 14% of the solids by weight. Oncethoroughly mixed, the mixture was discharged onto a pelletizer where theagglomeration process results in pellets of various size ranges fromless than 500 micron diameter to 50 mm (2 inch) diameter. Once thepellets are formed to a desired size range, the pellets are routed to adryer where the free moisture content is reduced to 0% to 4% by weight.The dried pellets are then processed through the screening equipment andcrushers to attain the desired SGN range.

In some instances the pellets are dried to a moisture content thatvaries between 0% and 2.5% to cure the pellet. Strengths of the pelletare adjusted based on the binder concentrations and point where thebinder is applied. In some circumstances the binder is added and themixer from 1% to 10% of the solids weight and in some instances thebinder is added on the pan pelletizer at 1% to 10% of the solids weight.

In one variation of the process, ground calcium carbonate powder isadded to the synthetic gypsum to increase the weight of pellets and toimprove pelletization process. Ground calcium carbonate is added atconcentrations between 1% to 5% by weight prior to the mixer in order toimprove the pellet formation. The ground calcium carbonate powder isground to a size that has a minimum of 90% passing a 325 mesh screen inorder for the powder to enhance the pellet formation and improve pelletgrowth on the pan pelletizer.

In one embodiment the recycle concentration is increased from 2% to 40%to improve the pellet strengths. Recycled pellets are crushed to a sizeof 1 mm or less and then added to the dried gypsum prior to mixing inthe pin mixer. The combination of recycled pellets and dried gypsum arethen mixed with an adjusted binder concentration to reach 1% to 10%binder with the binder fluid added at both the mixer and on the pan atvarious concentrations from 1% to 8% at each location.

Example 5

Tests have also been conducted spread width of pelletized syntheticgypsum according to the present invention. In one embodiment, 100 lbs ofsynthetic gypsum pellets having a SGN of 360 and a hardness of 2.5 kg(5.5 pounds) was fed through a feedgate having a 2 inch diameter to aspreader having a fan frame of 3.50 inches to 3.75 inches with finsettings of 1-2-1-2 spinning at speeds of 700 rpm, 750 rpm and 800 rpm.Wind conditions were north-north-west at 8 miles per hour (“mph”). Thevehicle carrying the spreader was traveling at 15 mph. Under theseconditions, the spread was 70 feet to 78 feet.

Example 6

Tests have also been conducted spread width of pelletized syntheticgypsum according to the present invention. In one embodiment, 100 lbs ofsynthetic gypsum pellets having a SGN of 299 and a hardness of 1.5 kg(3.3 pounds) was fed through a feedgate having a 2 inch diameter to aspreader having a fan frame of 3.50 inches to 3.75 inches with finsettings of 1-2-1-2 spinning at speeds of 700 rpm and 750 rpm. Windconditions were north-north-west at 8 miles per hour (“mph”). Thevehicle carrying the spreader was traveling at 15 mph. Under theseconditions, the spread was 65 feet to 75 feet.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention, andthat this invention not be limited to the specific constructions andarrangements shown and described, since various other changes,combinations, omissions, modifications and substitutions, in addition tothose set forth in the above paragraphs, are possible. Those skilled inthe art will appreciate that various adaptations, modifications, andcombinations of the just described embodiments can be configured withoutdeparting from the scope and spirit of the invention. Therefore, it isto be understood that, within the scope of the appended claims, theinvention may be practiced other than as specifically described herein.

1. A method of producing a fertilizer comprising: feeding syntheticgypsum to a forming device; feeding a binder composition to the formingdevice; and forming the material fed to the forming device to a meanpellet size guide number (SGN) from approximately 150 to approximately300, wherein the resulting pelletized synthetic gypsum has a crushstrength from approximately 2 lbf to approximately 12 lbf.
 2. (canceled)3. The method of claim 1, wherein the synthetic gypsum fed to theforming device has a mean particle size of less than 100 microns.
 4. Themethod of claim 1, wherein the binder composition comprises alignosulfonate.
 5. The method of claim 1, wherein the binder compositioncomprises a water soluble binder.
 6. The method of claim 1, wherein thebinder composition is selected from the group consisting of brewerscondensed solubles, sodium carbonate lignin, cane molasses, beet syrup,beet molasses, desugared beet molasses, whey, starch, starchderivatives, soy solubles with cane molasses, hydrolyzed collagen, aminoacid solutions, cellulose derivatives, and cellulose based polymerbinders.
 7. The method of claim 1, further comprising feeding anadditive to the forming device, wherein the additive is selected fromthe group consisting of ground calcium carbonate, calcium bentonite,kaolin clays, manganese, zinc, boron, calcium, copper, and elementalsulfur.
 8. The method of claim 7, wherein the additive compriseselemental sulfur.
 9. The method of claim 1, wherein the mean SGN is fromapproximately 250 to approximately
 280. 10. The method of claim 1,wherein the forming device comprises a pelletizer.
 11. The method ofclaim 1, wherein the forming device comprises a granulator or anextruder.
 12. A fertilizer made by the method of claim
 1. 13. Afertilizer comprising: pellets, the pellets comprising synthetic gypsumand a binder composition, the pellets further comprising mean pellet SGNfrom approximately 150 to approximately 300, wherein pellets have acrush strength from approximately 2 to approximately 12 lbf. 14.(canceled)
 15. The fertilizer of claim 13, wherein the bindercomposition comprises a lignosulfonate.
 16. The fertilizer of claim 13,wherein the binder composition comprises a water soluble binder.
 17. Thefertilizer of claim 13, wherein the binder composition is selected fromthe group consisting of brewers condensed solubles, sodium carbonatelignin, cane molasses, beet syrup, beet molasses, desugared beetmolasses, whey, starch, starch derivatives, soy solubles with canemolasses, hydrolyzed collagen, amino acid solutions, cellulosederivatives, and cellulose based polymer binders.
 18. The fertilizer ofclaim 13, wherein the pellets further comprise an additive, wherein theadditive is selected from the group consisting of ground calciumcarbonate, calcium bentonite, kaolin clays, manganese, zinc, boron,calcium, copper, and elemental sulfur.
 19. The fertilizer of claim 13,wherein the pellets further comprise an additive comprising elementalsulfur.
 20. The fertilizer of claim 13, wherein the mean SGN is fromapproximately 250 to approximately
 280. 21. A process for producing afertilizer comprising: feeding synthetic gypsum to a dryer; feedingdried synthetic gypsum and a binder composition to a mixer; mixing thematerial fed to the mixer; feeding the mixed material to a formingdevice; pelletizing the material fed to the forming device; feeding thepelletized material to a dryer; drying the pelletized material; feedingthe dried pelletized material to a screener; and screening the materialfed to the screener to a mean pellet size guide number (SGN) fromapproximately 150 to approximately 300, wherein the resulting pelletizedsynthetic gypsum has a crush strength from approximately 2 lbf toapproximately 12 lbf.
 22. The process of claim 21, further comprisingrecycling unders and overs removed during screening to the mixer. 23.(canceled)
 24. The process of claim 21, wherein the synthetic gypsum fedto the mixer has a mean particle size of less than 100 microns.
 25. Theprocess of claim 21, wherein the binder composition comprises alignosulfonate.
 26. The process of claim 21, further comprising feedingan additive to the mixer, wherein the additive is selected from thegroup consisting of manganese, zinc, boron, calcium, copper, andelemental sulfur.
 27. The process of claim 21, further comprisingfeeding an additive to the mixer, wherein the additive compriseselemental sulfur.
 28. The process of claim 21, wherein the mean SGN isfrom approximately 250 to approximately
 280. 29. A fertilizer made bythe process of claim 21.